The present invention relates to the art of interactive image-guided surgery. It finds particular application in conjunction with stereotactic surgery performed in CT imaging systems using a frameless mechanical arm to guide minimally invasive surgical tools and will be described with particular reference thereto. It is to be appreciated, however, that the invention is also applicable to robotic and other mechanical arm mechanisms used as frameless guidance assist devices in other imaging systems including ultrasonic and magnetic resonance imaging (MRI) devices.
Heretofore, several mechanical arm type mechanisms have been proposed in interactive imaging systems for guiding intervertional surgical tools to allow accurate placement of catheters, drainage tubes, biopsy probes, or the like, within a patient's body. U.S. Pat. No. 5,142,930 teaches a mechanical arm having a fixed base at a first end and a tool holder on the other end. The tool holder is adapted to hold and guide interventional surgical tools. The mechanical arm is associated with a computer coupled to a display device displaying one or more images from an image space of a patient's anatomy generated by an imaging device. The computer tracks the location of the surgical tool through physical space, performs a transforming rotation of the physical space to the image space, and causes the display device to show the location of the surgical tool within the image space. Optical encoders are arranged at each gimbal joint of the mechanical arm in order to detect rotational or angular movement of the arm segments for accurate tracking of the end tip of a tool relative to the position of fiducial implants disposed in or on the patient.
One disadvantage of the above system, however, is the need for a bulky stereotactic localization frame. Although the position of a tool carried on the arm relative to the base is accurately tracked, the use of fiducial implants remains necessary to initialize a mapping between the internal coordinate system of the surgical image and the external coordinate system of the mechanical arm. In addition, the arm described in the system identified above is allegedly easy to manipulate and use because the arm is counterbalanced using conventional weight balancing techniques.
A frameless stereotactic arm apparatus that does not rely upon the bulky localization frame or the fiducial implants placed on a patient would reduce the setup time spent before surgery. It would be desirable to provide a frameless stereotactic arm apparatus with multiple arm segments which are lockable into fixed locations so that precise orientation and accurate guidance of surgical instruments is possible. Preferably, the lockable frameless stereotactic arm apparatus would include frictional brakes at each movable joint for locking the arm into any desired conformation against the force of gravity, but which would permit movement of the arm in emergency situations in response to application of a force in excess of a predetermined breakaway threshold force.
U.S. Pat. No. 5,078,140 teaches a jointed robotic arm useful in precisely orienting surgical tools and other implements used in conducting stereotactic surgery or other related procedures on human body parts. The mechanical arm used in this system includes six rotatable joints and a set of servo motors for moving the arm into predetermined orientations. The servo motors include electromagnetic brakes that are activated whenever power is removed from the robotic arm. Further, all of the servo motors incorporate optical incremental encoders that provide position and velocity feedback to the servo system driving the arm into the above-noted predetermined orientations. A specialized computer program with control software continuously monitors the angles and positions between all of the joints of the arm in relation to each other and in relation to a base member which is affixed to a metal ring member of a head frame fixed to a patient's head. The robotic arm includes a "free" mode which is useful for decoupling the servo motors from active servo control so that the arm may be manually manipulated.
One disadvantage, however, of the above stereotactic surgical system is that the mechanical arm must necessarily be connected to a rigid frame apparatus supported by the scanning table and attached to a relatively immovable body part of a patient, usually the head. The frame is bulky and often interferes with access to some parts of the patient's anatomy. It would, therefore, be desirable to provide a frameless stereotactic arm apparatus connected from overhead directly to an imaging apparatus rather than to a patient's head or to a stereotactic head frame, or the like.
The present invention provides a new and improved frameless stereotactic arm apparatus and method of using same for planning and executing image guided interventional procedures which overcomes the above-referenced problems and others.